Over the moon: the effect of the lunar cycle on three species of newt in the UK

Lunar cycles provide several cues that can be recognised by animals, such as changes in light intensity, gravity and geomagnetism, all of which have been linked to changes in behaviour. Although amphibians are known to use celestial cues in orientation, the influence of the lunar cycle on amphibian behaviour has received comparatively little attention. The aim of this study was to determine whether the lunar cycle influences the capture rate and activity of three newt species: the great crested (Triturus cristatus), smooth (Lissotriton vulgaris) and palmate newts (Lissotriton helveticus). This study also aimed to discover how other external factors, including water temperature, light level and cloud cover influenced the capture rate and activity of each species. Capture data from a 9-year study was firstly used to identify how capture rates were influenced by the lunar cycle and external factors. This was then followed by a study focussing on two lunar cycles in 2019, which utilised results from trap captures and activity monitoring to determine the influence of the lunar cycle and external factors. During the 9-year study this study a combination of both lunar phase and temperature influenced the capture rates of newts, but with different combinations of factors important in different species. Likewise, over two complete lunar cycles in 2019, a combination of environmental factors influenced trapping rates, and this appeared to be species-specific. Direct observations on activity revealed that lunar phase, water temperature and light level all had an influence on the activity on each of the three newt species. In great crested newts there was increase in activity at higher temperatures and around both the full and new moon, whereas smooth and palmate newts were more likely to be active during periods of high illumination. Evidence for both capture rate and activity being influenced by multiple external factors means that surveys of newts may be biased unless they can account for each of these factors. However, in high density populations of newts such as that studied here, interspecific interactions, limited space for newts within a trap and escapes from traps may mean capture rates are not reliable indicators of activity. I recommend that surveyors should take external factors, including influences of the lunar cycle, into account when interpreting and comparing results of newt surveys.